Graphite is a well-known mineral consisting of the element carbon, crystallizing in the hexagonal system. It is black, opaque and very soft being widely used due to its property of good conductivit of electricity. It has a greasy feel and rubs off on anything it touches, leaving a black mark. As an artificial product, graphite is known as scales in gray pig iron and as graphitic powder formed in iron furnaces. It is also produced on a large scale in electric furnaces. It is widely used in refractory, as a constituent in the lubricants manufacture, foundry, brake linings, facings, packings, pencils, batteries and carbon brushes. Active carbon is well-known for its absorption property of various solvents or as a filter media. However it is unsuitable for absorption of from water, since after absorption it sinks and can not be easily removed. The same problem of sinking exists with magnesium oxide, also known for its absorption property. But, again, due to its sinking it can not be used for absorption of petroleum products on water caused by spillage.
Polyurethane foam in the form of small pieces was suggested in a recent French Pat. No. 2,605,014 to be useful for absorbing oil from water However, the absorption power of urethane is quite low and therefore the ratio of polyurethane to oil is high. Moreover, a significant part of the urethane powder is wasted.
Expanded graphite was disclosed in a number of references possessing improved properties for specific uses. Thus in a review by D.D.L. Chung [Journal of Material Science 22, (1987), p. 4190-8] expanded graphite, obtained by exfoliation, is described by a process in which graphite expands by up to hundreds of times along the "C" axis, resulting in a puffied-up material with a low density and a high temperature resistance. This type of exfoliated graphite is mentioned to be useful for high-temperature gaskets, packings, fire extinguisher agent, thermal insulator, as a conductive resin composite -- in composition with a thermoplastic resin -- and as a chemical reagent. It is also mentioned its use as an adsorbent for gas chromatography and as a substrate for the study of adsorbed films.
In the Japanese Patent Application No. 8869705, Kisch graphite is mixed with natural graphite at 90.degree. C. and treated with sulfuric acid in the presence of an oxidizing agent (such as a peroxide), heated at a temperature above 800.degree. C. and rolled into sheets. It is claimed that the resulted sheets possess high resilience and chemical resistance.
According to U.S. Pat. No. 3,357,929 a vermicular expanded graphite structure is described for absorption of various liquids, such as: water, hydrocarbons, silicones halocarbons, strong acids, strong alkalies and liquid halogens. Nothing is mentioned in this patent on a selective absorption, the data presented therein referring only on the maximum amount of various liquids absorbed by the graphite. As mentioned in Example 1, the graphite absorbs more water than any known sorption agents. As mentioned in Table 1 of this patent, the expanded graphite absorbed 46.7 g of water per gram compared with 29 gram of kerosene per gram of the same expanded graphite.
In the U.S. Pat. No. 4,961,988, a packing of expanded graphite is prepared by the embedment of organic synthetic films, glass fibers, synthetic fibers and carbon fibers. The product obtained is mentioned to be useful as a sealing material for fluid media.
According to the U.S. Pat. No. 3,338,815, a particular type of graphite having a surface area of at least 50m.sup.2 /g is mentioned to possess the property of separating longchain normal hydrocarbons having at least ten carbon atoms by a preferential absorption of a particular hydrocarbon present therein. It is further mentioned, that the hydrocarbons may be present in an organic solvent. But nothing is mentioned in this patent on the preferential absorption of the particular type of graphite of a hydrocarbon present in a water media.
It is an object of the present invention to provide a particular structure of expanded graphite possessing a selective high absorption power of petroleum products. It is another object of the present invention to provide a particular structure of expanded graphite, which has the property of absorbing in a selective manner, only petroleum products from a water media without absorbing water. It is yet another object of the present invention to provide a particular structure of expanded graphite, which after the selective absorption of petroleum products, is able subsequently to release the absorbed materials by a simple squeezing.